linux-kernel - Re: [PATCH V1 4/6] dt-bindings: Add xen,dev-domid property description for xen-grant DMA ops

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Date:   Mon, 2 May 2022 16:59:45 -0500
From:   Rob Herring <robh@...nel.org>
To:     Oleksandr Tyshchenko <olekstysh@...il.com>
Cc:     xen-devel@...ts.xenproject.org,
        virtualization@...ts.linux-foundation.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Jason Wang <jasowang@...hat.com>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Julien Grall <julien@....org>, Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH V1 4/6] dt-bindings: Add xen,dev-domid property
 description for xen-grant DMA ops

On Fri, Apr 22, 2022 at 07:51:01PM +0300, Oleksandr Tyshchenko wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> 
> Introduce Xen specific binding for the virtualized device (e.g. virtio)
> to be used by Xen grant DMA-mapping layer in the subsequent commit.
> 
> This binding indicates that Xen grant mappings scheme needs to be
> enabled for the device which DT node contains that property and specifies
> the ID of Xen domain where the corresponding backend resides. The ID
> (domid) is used as an argument to the grant mapping APIs.
> 
> This is needed for the option to restrict memory access using Xen grant
> mappings to work which primary goal is to enable using virtio devices
> in Xen guests.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> ---
> Changes RFC -> V1:
>    - update commit subject/description and text in description
>    - move to devicetree/bindings/arm/
> ---
>  .../devicetree/bindings/arm/xen,dev-domid.yaml     | 37 ++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
> 
> diff --git a/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml b/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
> new file mode 100644
> index 00000000..ef0f747
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/xen,dev-domid.yaml
> @@ -0,0 +1,37 @@
> +# SPDX-License-Identifier: (GPL-2.0-only or BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/arm/xen,dev-domid.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Xen specific binding for the virtualized device (e.g. virtio)
> +
> +maintainers:
> +  - Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
> +
> +select: true

Do we really need to support this property everywhere?

> +
> +description:
> +  This binding indicates that Xen grant mappings scheme needs to be enabled
> +  for that device and specifies the ID of Xen domain where the corresponding
> +  device (backend) resides. This is needed for the option to restrict memory
> +  access using Xen grant mappings to work.
> +
> +properties:
> +  xen,dev-domid:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description:
> +      The domid (domain ID) of the domain where the device (backend) is running.
> +
> +additionalProperties: true
> +
> +examples:
> +  - |
> +    virtio_block@...0 {

virtio@...0

> +            compatible = "virtio,mmio";
> +            reg = <0x3000 0x100>;
> +            interrupts = <41>;
> +
> +            /* The device is located in Xen domain with ID 1 */
> +            xen,dev-domid = <1>;

This fails validation:

Documentation/devicetree/bindings/arm/xen,dev-domid.example.dtb: virtio_block@...0: xen,dev-domid: [[1]] is not of type 'object'
        From schema: /home/rob/proj/git/linux-dt/Documentation/devicetree/bindings/virtio/mmio.yaml

The property has to be added to the virtio/mmio.yaml schema. If it is 
not needed elsewhere, then *just* add the property there.

Rob